Checked it out, and they do indeed have 13x19 and 17x22 ready fits, which would fit the OP's rather unusual plan to frame paper size identical to frame size. The vendor suggests using their product mat-less as far as I can see, with the utility of removing a side and replacing the print. But with spring-loaded back holding print against glass, would seem that removing the back is the only (and easiest way, IMO). The problem here is a print directly against glass without a mat - not a good idea.

Maybe the OP plans on using a single mat with small margins and just replacing the print periodically. I can see the utility of this, as if the paper fits snugly (but not too snuggly!) in the frame, hinging/acrylic corners or other fixation to back or mat are not needed.